1. Field of the Invention
The present invention relates to an optical receiver module having a light receiving device that converts an optical signal into an electrical signal.
2. Description of the Background Art
In optical communication systems using light as an optical transmission means, optical receiver modules having light receiving devices for converting optical signals into electrical signals are used as receiving equipment for receiving optical signals through optical transmission lines such as optical fiber lines (Refer to Japanese Patent Application Publication No. 9-54228).
FIG. 9 is a partly cutaway side view showing the configuration of an example of a conventional optical receiver module. The optical receiver module 6 is a coaxial-type module in which a photodiode 65 serving as a light receiving device and the like are placed in a housing 60 such as a metal package. Inside the housing 60 of the optical receiver module 6, the photodiode 65, a ferrule 61, and a converging lens 63 are arranged such that their optical axes are aligned with one another. An optical signal inputted through an optical fiber 62 extending in the ferrule 61 is incident on a photodiode 65 via the converging lens 63, and is then converted to an electrical signal for output.
FIG. 10 is a cross-sectional side view of another conventional optical receiver module. FIG. 11 is a top plan view of the optical receiver module shown in FIG. 10. The optical receiver module 7 is a surface-mount type module in which a photodiode 80 and an optical waveguide element 85 having an optical waveguide 86 that transmits an inputted optical signal to the photodiode 80 are placed on a substrate 70
In the optical receiver module 7, a ferrule 90, the optical waveguide element 85 having the optical waveguide 86, and the photodiode 80 are arranged such that their optical axes are aligned with one another. An optical signal inputted through an optical fiber 90 extending in the ferrule 61 is incident on a photodiode 65 via the optical waveguide, and is then converted to an electrical signal for output. In the coaxial optical receiver module 6 shown in FIG. 9, the size is increased because of the three-dimensional structure, and this limits cost reduction. In contrast, in the surface-mount type optical receiver module of FIGS. 10 and 11, the size and cost of the module can be reduced. In an optical receiver module, an amplifier device may be provided for amplifying and outputting an electrical signal that has been converted from an optical signal by a light receiving device. In the coaxial optical receiver module 6 shown in FIG. 9, optical elements such as the converging lens 63, etc. and the ferrule 61 are placed upstream (upper side) of the photodiode 65, and a metal base of the housing 60 is located downstream thereof (lower side).
In the optical receiver module 6 having such a configuration, an amplifier device is placed outside the housing 60, or distanced from the photodiode 65 inside the housing 60. In this case, the connection length between the photodiode 65 and the amplifier device is long, and this increases the size of the module. Moreover, it is difficult to amplify the electrical signals from the photodiode at high speed, because of the impedance of a wire between the photodiode 65 and the amplifier device.
In the case where an amplifier device is provided in the surface-mounted optical receiver module 7 shown in FIGS. 10 and 11, the substrate 71 is placed on the downstream side relative to the photodiode 80, and the amplifier device 81 is mounted on the substrate 71. However, in such a configuration, it is difficult to sufficiently shorten the connection length between the photodiode 80 and the amplifier device 81. Moreover, since it is necessary to secure a space to provide the amplifier device 81 in addition to the optical waveguide element 85 and the photodiode, the optical receiver module is increased in size.
In recent years, optical transmission systems have been required to increase the transmission data-rate at which optical signals are transmitted for communication, for example, from 1 Gbps to 5 Gbps. Optical receiver modules for receiving optical signals are similarly required to have a higher transmission data-rate. In addition, in order to achieve optical communication systems capable of efficiently conducting multiple communications, size reduction of optical modules, such as an optical receiver module, is necessary.
The present invention has been made to meet the above requirements, and an object of the present invention is to provide a compact optical receiver module capable of high-speed receiving of optical signals.
In order to achieve the above object, the present invention provides an optical receiver module comprising: a light receiving device placed on a substrate and used for converting an optical signal into an electrical signal; an optical transmission line placed on the substrate together with the light receiving device and used for transmitting and inputting the optical signal to the light receiving device; and an amplifier device placed at a predetermined position on the same side as the optical transmission line with respect to the light receiving device, and used for amplifying the electrical signals converted by the light receiving device.
The light receiving device used in the optical receiver module may be a photodiode.
The optical transmission line may be a planar surface optical waveguide. Alternatively, the optical transmission line may be an optical fiber or an optical fiber covered with a ferrule.
In the optical receiver module, N-number (N is an integer of two or more) of said light receiving devices may be arranged in parallel, and N-number of said optical transmission lines and N-number of said amplifier devices may be arranged in parallel corresponding to said N-number of light receiving devices.
This makes it possible to receive multi-channel optical signals by the single optical receiver module, and to further reduce the size of the optical receiver module per optical signal.
A submount for mounting the amplifier device thereon may be provided between the amplifier device and the optical transmission line. This enables the amplifier device to be placed together with an optical transmission line at a suitable position on the same side as the optical transmission line relative to the light receiving device.
A metal lead frame may be provided as an electrical connecting means for directing electrical signals amplified by the amplifier device to the outside. This allows the electrical signals to be read from the outside of the optical receiver module in a preferable manner.
The light receiving device, the optical transmission line, and a predetermined optical path through which an optical signal passes may be covered by molding of a transparent resin. Alternatively, the entirety of the optical receiver module containing the substrate, the light receiving device, the optical transmission line, and the amplifier device may be molded with a resin. In this case, the components of the optical receiver module can be held reliably.
As described above in detail, the optical receiver module of the present invention has the following advantages. The above optical receiver module has a surface-mounted structure in which the light receiving device and the optical transmission line are placed on the substrate, and the amplifier device for amplifying the electrical signals is placed on the same side as the optical transmission line (upstream side) with respect to the light receiving device. Consequently, it is unnecessary to secure a space to provide the amplifier device in addition to the space for the optical transmission line and the light receiving device, and hence the size and the production cost of the module can be reduced.
Since the amplifier device can be placed close to the light receiving device, the connection length between the light receiving device and the amplifier device can be reduced substantially. Consequently, the impedance of wiring between the light receiving device and the amplifier device is reduced, and the electrical signals from the light receiving device can be amplified at high speed. As a result, it is possible to achieve an optical receiver module capable of high-speed receiving of optical signals.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.